1. Field of Invention
This invention is directed to the field of semiconductors. More particularly, this invention is directed to group III-V nitride epitaxial semiconductor films for use in blue light emitting optoelectronic devices and also to a method of forming structures including the semiconductor films.
2. Description of Related Art
High-efficiency solid-state optoelectronic devices based on group III-V nitrides have a sufficiently wide bandgap for short-wavelength visible light emission. For example, the Al--Ga--In--N system has a bandgap which covers the entire visible spectrum. III-V nitrides have been used in short-wavelength light-emitting diode (LED) devices to provide bright green-to-ultraviolet light at high efficiencies. InGaN is used in green and blue LEDs. LEDs cover all three primary colors of the spectrum (red, green and blue) and accordingly can be used in various combinations to produce any color. III-V nitrides have also been used in diode lasers that operate at room temperature and emit visible light in the blue-violet range under continuous operation. These diode lasers emit coherent radiation and focus light into smaller spots, enabling higher-density optical data storage and higher-resolution printing. Blue semiconductor lasers are especially promising for such applications due to their reduced wavelength. These lasers can potentially be combined with green and red lasers to create projection displays and color film printers.
III-V nitrides provide the important advantage of having a strong chemical bond which makes them highly stable and resistant to degradation under high electric current and intense light illumination conditions that are present at the active regions of optoelectronic devices. These materials are also resistant to dislocation formation once grown.
Due to the high growth temperatures of III-V nitrides, there are presently only a limited number of known substrates suitable for supporting nitride film growth. The most commonly used substrate materials are sapphire and silicon carbide. These materials have significantly different lattice parameters and thermal expansion coefficients than the III-V nitrides. Consequently, the interfaces formed between the substrates and nitrides lack coherence, resulting in increased interface strain and interface energy, and diminished film wetting. These factors largely affect the nitride film growth process and the quality of the resulting nitride films. For example, the growth process of III-V nitrides on sapphire using known processes is highly three-dimensional. III-V nitride film growth occurs initially by the formation of discrete three-dimensional nitride islands on the substrate. These islands grow and coalesce with each other. Lattice matching is poor at the regions of the film at which the islands coalesce. High dislocation densities are generated at these regions. Dislocation arrays in the nitride film adversely affect the optoelectronic properties of devices fabricated on the nitride films by affecting carrier recombination processes in the active regions of the devices, and ultimately reducing emitted light intensities and device efficiencies.